Laser printers, digital printing presses, copiers, fax machines, plate setters, direct-to-film laser printers, scanned laser displays, other printing and display devices and some systems used for the fabrication of electrical circuits, use a plurality of light sources to emit light that is scanned across a medium. The light produces a number of exposed scan lines on the medium where the medium has been altered by the light to form a latent image. The scan lines can suffer from a number of errors which may be caused by the optical system used to produce the scan lines on the photosensitive medium, for example due to an aberration such as distortion in the optical system.
Dry toner laser printers, liquid electrophotographic (LEP) laser printers and LED printers (to name only some printers) generally use a discharge area development (DAD) electrophotographic process in which light is used to selectively discharge electrical charge on a photoconductor to form a latent electrostatic image. Electrically charged toner or ink is then applied to the photoconductor and adheres to the photoconductor in exposed regions in which the electrical charge has been discharged but does not adhere in unexposed image regions which have not been discharged. The adhered toner or ink is then transferred to a print medium such as paper and fused onto the print medium. Errors in the scan lines produced on the photoconductor can produce visible artifacts in the printed image on the print medium, which are undesirable. Some electrophotographic devices use charge area development (CAD), for example, many photocopiers use CAD.
For electrophotographic printers, a certain exposure energy density, for example measured in μJ/cm2, is necessary to adequately discharge the electrical charge on the photoconductor. The exposure energy density for a particular region of photoconductor can be regarded as the product of the power density (normally measured in mW/cm2) of the light incident on the photoconductor and the exposure time of the photoconductor by the light for that region of the photoconductor. The process speed of the printers is, at least in part, limited by the exposure time that is necessary to adequately discharge the electrical charge on the photoconductor.
Some systems used for the fabrication of electrical circuits scan light onto a substrate to produce a scan line on the substrate by means of a photochemical reaction. A minimum exposure energy density may be required for the light incident on the substrate in order that a circuit can be properly manufactured. Artifacts resulting from scan line errors may be detrimental to the performance of the electrical circuit that is produced.